In a duplex web-fed printer such as described in United States patent U.S. Pat. No. 5,805,967 (De Bock et al. / Xeikon NV), and European patent specification EP 0871082 (Xeikon NV), moving transfer surfaces in the form of transfer belts carry toner particle images to transfer stations at which the images are transferred to opposed faces of a paper web. The paper web passes through nips at the transfer stations.
It is often desirable to ensure registration of the image printed on one face of the web with the image printed on the opposite face of the web. This can be particularly the case when the web is formed of a transparent or semi-transparent material and/or perforations or other physical modifications extending through the web material need to be aligned with specific parts of both images.
It is an objective of the present invention to enable such back-to-back registration to be achieved in a simple manner.